1. Field of the Invention
The present invention relates to a purge control system to be used in conjunction with an electronics enclosure. More particularly, the present invention relates to a purge control system for use in hazardous areas to create a non-hazardous or non-explosive atmosphere within an electrical instrument enclosure.
2. Prior Art
It is often necessary to use electrical measurement devices or the like in a hazardous environment such as a drilling rig area, refinery or coal mine. These hazardous environments usually contain a mixture of natural gas that can explode if electrical equipment is activated. Therefore methods or systems have have been developed to make electrical equipment "safe" to use. These safe environments include explosion-proof enclosures, equipment submerged in oil or other substances, or purged enclosures.
A preliminary search was conducted on the above, and the following prior art U.S. patents were uncovered:
______________________________________ U.S. Pat. No. Patentee Issue Date ______________________________________ 3,703,192 Staudacher et al. November 21, 1972 3,777,928 Kober December 11, 1973 4,301,113 Alguire et al. November 17, 1981 3,989,461 Skocypec et al. November 2, 1976 4,317,797 Smith March 2, 1982 4,228,197 Means October 14, 1980 ______________________________________
An alarm and safeguard system for a controlled environment box is disclosed in U.S. Pat. No. 3,703,192 to Staudacher et al. The purpose of the Staudacher patent is to provide a "dry box" for the preparation of various compounds which would spontaneously ignite if exposed to oxygen and moisture. This device employs electrical switches, an open manometer, and other electrical devices which are not allowed in a hazardous area.
In U.S. Pat. No. 3,777,928 to Kober a process and apparatus for purging gas storage tanks is disclosed. The Kober process is primarily concerned with the purging of gas or air on board tanker ships by generating an inert purging gas. This apparatus contains a generator which includes a burner, scrubber and condenser unit, all of which would be restricted in a hazardous area.
A system for circulating a particular gas through a chamber is disclosed in U.S. Pat. No. 4,301,113 to Alguire et al. The Alguire invention is used to circulate a flammable biocidal gas through a reaction chamber without the presence of electrical equipment. An assembly attachment to a sterilizing chamber is provided with circulating means which avoid the use of electrical motors and switches.
No prior art apparatus provides a pneumatic control system which maintains an over-pressure in an enclosure to prevent the entry of hazardous gases. No prior art device is approved for use in a Class I, Division I hazardous environment to control the internal atmosphere of an electronics housing.